1. Field of the Invention
The present invention relates in general to a method for purification of water-soluble non-ionic contrast agents. More particularly, the present invention relates to a process for the purification by chromatographic technique of water-soluble non-ionic contrast agents from a raw water-soluble non-ionic contrast agent solution.
2. Description of the Related Art
Water-soluble non-ionic contrast agents are usually used in medical treatment, especially in neurography, angiography, encephalography, enhanced computed tomography, and urography. As compared with the ionic contrast agent traditionally used in medical treatment, the non-ionic contrast agent has a lower incidence of side effects and complications.
However, the synthesizing steps of the non-ionic contrast agent are more complicated than those of ionic contrast agents, especially the purification step, because the non-ionic contrast agent cannot be purified from water solution by deposition like ionic contrast agents. Hence, removing the inorganic salts from the final reaction solution to enhance the yield of the product is the encountered problem.
The compound (s)xe2x80x94N,Nxe2x80x2-bis(1,3-dihydroxyisopropyl)-5-lactylamido-2,4,6-triiodoisophthalamide (Iopamidol) is water-soluble. If Iopamidol is used for medical treatment, it must be purified after synthesis. However, Iopamidol""s yield is not optimum. In CH 608189, Iopamidol is separated from the final reaction solution by alternating with cation exchange resin and anion exchange resin, and the yield is only 65%. In DE 19507294, Iopamidol is purified by alternating with strong base anion exchange resin and weak base anion exchange resin, and the yield is 82.7%. These methods cannot provide sufficient yield. If the yield is enhanced, costs are reduced.
The present invention provides a process for the purification of water-soluble non-ionic contrast agents using simple chromatographic technique. Yield is enhanced and costs are reduced.
The present invention provides a process for the purification of water-soluble non-ionic contrast agents from water-soluble non-ionic impurities. At first, a raw water-soluble non-ionic contrast agent solution is injected on a chromatographic column containing non-ionic resins. The deionized water acts as a first eluent, and a plurality of water-soluble impurities contained in the raw water-soluble non-ionic contrast agent solution are eluted with deionized water. The water-soluble non-ionic contrast agent is then eluted with alcohol.
In the present invention, the non-ionic contrast agent is synthesized using the method disclosed in Swiss patent No. 1,472,050 by Savac A. G. After iodination, acid chloride formation synthesis, chiral synthesis, amidation, and base hydrolysis, the obtained raw non-ionic contrast agent solution has numerous water-soluble impurities, including polar aprotic solvents, inorganic salts, water, and by-products. The polar aprotic solvent can be N,N-dimethyl acetamide (DMA) or N,N-dimethyl formamide (DMF). The solubilities in water of these impurities and the non-ionic contrast agent are similar. Therefore, it is difficult to obtain the non-ionic contrast agent by crystallization. In order to solve such problems, the present invention provides a separation method using non-ionic resin to effectively separate the water-soluble non-ionic contrast agent from water-soluble impurities.
In the present invention, the chromatographic column is packed with non-ionic resins, and then used to purify the water-soluble non-ionic contrast agent. The preferred non-ionic resins have favorable interaction with the water-soluble non-ionic contrast agent. The non-ionic resins can be polystyrene, polystyrene derivatives, polymethacrylate or polymethacrylate derivatives.
The raw water-soluble non-ionic contrast agent solution comprises water-soluble non-ionic contrast agents and water-soluble impurities. The water-soluble impurities include polar aprotic solvents, inorganic salts, water and by-products. At the first stage, deionized water acts as a first eluent and the raw water-soluble non-ionic contrast agent solution flows through the chromatographic column containing non-ionic resins. Because a strong interaction exists between the water-soluble non-ionic contrast agents and the non-ionic resins, the water-soluble non-ionic contrast agents stay in the chromatographic column. The other polar aprotic solvents, inorganic salts, water and by-products are then eluted out. At the second stage, alcohol acts as a second eluent so as to elute the water-soluble non-ionc contrast agent.
The process of the present invention is used for the purification of water-soluble non-ionic contrast agents from water-soluble non-ionic impurities. The water-soluble non-ionic contrast agent is a radiation ray contrast agent, such as:
(s)-N,Nxe2x80x2-bis(1,3-dihydroxyisopropyl)-5-lactylamido-2,4,6-triiodoisophthalamide (Iopamidol);
N,Nxe2x80x2-bis(2,3-dihydroxypropyl)-5-[N-(2,3-dihydroxypropyl)acetamido]-2,4,6,-triiodoisophthalamide (Iohexol);
N,Nxe2x80x2-bis(2,3-dihydroxypropyl)-5-[N-(2-hydroxyethyl)-glycolamido]-2,4,6,-triiodoisophthalamide (Ioversol); and
5,5xe2x80x2-[malonylbis(methylimino)]bis[N,Nxe2x80x2-bis[2,3-dihydroxyl-1-(hydroxymethyl)propyl]]-2,4,6-triiodoisophthalamide (Iotrolan).
The chromatographic column is packed with non-ionic resins. The non-ionic resins can be polystyrene, polystyrene derivatives, polymethacrylate, polymethacrylate derivatives, or other having strong interaction with the non-ionic contrast agents.
After the non-ionic resins are uniformly and closely packed into the chromatographic column, the deionized water flows through the chromatographic column to condition the non-ionic resins. Then the final reaction solution, that is, the raw water-soluble non-ionic contrast agent solution, is injected on the chromatographic column. An appropriate amount of deionized water is used to elute the impurities. With regard to the water-soluble non-ionic contrast agent, it is absorbed on the non-ionic resin in the chromatographic column.
The remaining water-soluble non-ionic contrast agent is eluted with alcohol having a low carbon number. The alcohol has great dissolving ability for the non-ionic contrast agent, and can be C1-6 alcohol, such as methanol, ethanol, n-butanol, and iso-butanol.
After eluting with alcohol, the correcting eluate is treated by condensing, re-crystallizing et al. steps. The purity of the obtained non-ionic contrast agent is over 99.7%.
Without intending to limit it in any manner, the present invention will be further illustrated by the following examples.